diesel engine seems too easy to turn over by hand

[AW10]

A mate and I are in the process of replacing the headgasket on a 54 plate Shogun Sport (4D56 4 pot turbo diesel). I was turning the engine over by hand to get all of the timing marks lined up and I was surprised how easy it was to turn it. With its higher compression ratio than a petrol engine I was expecting to really have to put some effort in on the compression stroke but it was surprisingly easy and no air leaks could be heard. As the engine isn't running and the fuel pump is off is compression pressure leaking out of the injectors or something similar? The fault we're trying to resolving is oil in the coolant; the engine otherwise runs well and it will cruise happily at 75 or so.

Edited by AW10 on Tuesday 17th October 20:01

[stevieturbo]

if the head is in place, injectors in place, glow plugs in place, etc etc then yes you should feel some compression somewhere.

Are you rotating very small amounts, or full turns ?

[AW10]

The head is still in place and torqued down. Injectors and glow plugs untouched. Turned it a full crank revolution to get all three marks lined up - a petrol engine would have been much harder to turn. So a bit puzzled.

[andburg]

Remove a glow plug and do a compression test…sounds rather wrong

[AW10]

I hear what you both say but it runs fine and pulls well with no smoke from the exhaust. It starts right up and idles smoothly, at least as smoothly as an old tech diesel ever does. That’s the bit that doesn’t correlate.

[Darkslider]

Have you checked the valve clearances before turning it over? The last 4D56 I did in an L200 had adjustable tappets and I got a bit of carbon from the inlet tract/manifold in amongst the cams and it stopped a few of the valves from completely seating. It's a long shot this is your issue but a compression/leak down test would show it up straight away.

[GreenV8S]

andburg said:

Remove a glow plug and do a compression test…sounds rather wrong

That can turn into a bit of a job on some engines - I'm not sure I'd take the risk given that the engine appears to be running fine.

[AW10]

We will just be changing the head gasket and otherwise leaving what seems to be well enough alone.

The head came off yesterday without much of a fight. There was a lot of engine oil between the block and the gasket which would seem to confirm our diagnosis. Otherwise everything looked OK and no other signs of trouble. Some internet research suggests that pattern part head gaskets are a false economy; it was a Victor Reinz one that came out. So new one ordered from the main dealer and will go in early next week. I’m curious to see if the engine feels any different to turn over by hand after the new gasket is fitted.

[stevieturbo]

Reinz sell aftermarket as well, and some other re-sellers often just re-package the Reinz gaskets anyway

But yes, always try and go for OE gaskets like that vs cheap unknown

[AW10]

So a bit of an update… we replaced the head gasket with a genuine old from the main dealer and put the head back on. After putting the timing belt back on we turned the engine over by hand a few times to make sure all was well with the timing and compression could be heard leaking out as you would expect and kickback could be felt as well. It started up first time and runs fine. It feels like it has a bit more power but with the wet roads I didn’t really try very hard. No more oil in the overflow bottle but some black water which will just be residual oil in the the cooling system. We’ll do another flush or two and that will hopefully be the end of it.

[AW10]

And a further update… although never putting many rice puddings in danger the Shogun has performed just fine for some 1600 miles and it’s been renamed the shogone because it’s in Ukraine doing some good there. Thanks again for the help.